Burnham SteamMax STMX075

The SteamMax STMX075 is one of the twelve sizes in U.S. Boiler Company's current SteamMax gas-fired steam line. Its PDS ratings row prints 75 MBH input, 62 MBH output and a 47 MBH net AHRI steam rating covering 169 sq ft (1.333 piping and pickup allowance), at 82% AFUE.

The boiler uses a cast-iron sectional design with metal push nipples, wide internal waterways, heat transfer pins below the water line, no heat transfer pins above the water line and a large steam chest, with optimized stainless steel burners, a step-opening gas valve, a probe-type low-water cut-off, an industrial-grade pressuretrol, a rear low-profile draft diverter, a vent damper (models 075–299) and 2 in. risers. Supply and return are 2 in. NPT with a 2 in. skimming port tapping, the gas connection is 1/2" NPT, and the unit ships with a 15 PSI relief valve and gauge glass; near-boiler piping kits are documented for the residential sizes.

The 100–550 MBH sizes are documented as residential builds with combustion controls and continuous-retry ignition (Honeywell S8610M). U.S. Boiler prints a 10-year limited heat exchanger warranty and a 10-year limited waterside corrosion warranty. No official Canadian-sales statement was found, so canadianStatus stays 'unknown', and gas, combustion and steam work belongs with a licensed contractor.